Containers for the dispensing of consumer products such as medicines, foods, etc. which utilize screw top and snap cap closures, are typically sealed to prevent tampering with the goods therein prior to ultimate purchase by the consumer. Over the past few years, and especially in the United States, such tampering with goods has occurred, resulting in injury, often severe, and in some cases, even death. Accordingly, it has become apparent that more effective systems for the sealing of such containers are necessary.
One system which has met with significant commercial success bears the trademark "Safe-Gard". This system provides a hermetic seal that is suitable for use with ingestible commodities. The seal is particularly effective for products which should preferably be kept free from contamination, oxidation, and/or moisture.
The seal employed in the "Safe-Gard" system typically comprises in order from top to bottom: a pulp board backing, a wax coating, aluminum foil, and a heat sealable polymeric film coating. These materials are typically supplied in strip form as a laminated structure, and applied to a filled container in conventional fashion during the filling process. After being capped, the filled container is passed through an electromagnetic field generated by induction heating equipment, which heats the outer edge of the aluminum foil, thereby bringing about the melting of the heat sealable polymeric film coating. After the container is removed from the induction field, the heat sealable coating will cool and the foil will be hermetically sealed to the lip of the container. During the induction heating step, the wax coating between the foil and pulpboard backing also melts, destroying the bond therebetween. While the wax remains in a molten state for a short period of time, it is wicked up or absorbed by the pulpboard backing such that the wax bond is permanently weakened. Upon removal of the cap from the container, the pulp backing remains with the cap's inner surface, which contacts and seals the lip of the container after the foil liner has been removed by the consumer.
It has been found that the heat sealable polymeric film coating presently utilized in the container industry has a relatively weak bond to containers currently used in high speed container-filling industries, such as the food industry. Furthermore, it has been found that the commercially available heat sealable polymeric film coatings or adhesives can be ineffective for use with various container materials in the induction innerseal system. For example, while an adhesive may be highly effective for polyethylene containers, it may be relatively ineffective with other conventional plastic containers, such as polystyrene or polypropylene. Furthermore, while an adhesive may be effective for plastic containers, it may be ineffective for glass containers. Additionally, most commercially available adhesives useful in induction innerseal systems are not useful for containers having metal caps, because these caps dissipate much of the energy available for sealing the adhesive.
It has now been discovered that the polymeric composition of this invention, when utilized in an induction-activated innerseal system, will provide a strong, heat-sealed bond on glass containers and most popular plastic containers, such as polystyrene, polyethylene, polypropylene, polyvinyl chloride, etc., regardless of whether the container has a plastic cap or a metal cap.